Sure, but just because it’s chock full of Hydrogen, which happens to be about the same mass as a neutron and thus takes up a lot of its energy per collision. Plastic, being a hydrocarbon, does the same thing.

That being said, water is pretty cool. You could use 2 inches of lead to stop 90% of gamma radiation, or 2 feet of water for the same effect. On top of that, metal is terrible at slowing neutrons (due to metal not being hydrogen), but that same 2 feet of water will slow down the neutrons by about 99.5%.

Cream of tartar is a type of acid, and is usually used in baking as along with baking soda as a leavener. Baking powder is generally just baking soda and cream of tartar mixed together, but some recipes call for adding them separately in different ratio then you would find in baking powder.